This invention relates to a magnetic recording member having a high coercive force.
A known magnetic recording member having a high coercive force in the inner planar direction is widely used as a hard disc medium on which high-density recording is possible This known magnetic recording member is manufactured by first forming a Cr film on a non-magnetic substrate made of, for example, aluminum, and them forming on the Cr film a Co alloy film, by a vacuum deposition or sputtering method.
The coercive force in this prior art magnetic recording member is generated by the following mechanism. When a Cr film is formed on a non-magnetic substrate by vacuum deposition or sputtering, the obtained Cr film contains columnar crystal grains in which the (110) plane of the bcc (body-centered cubic) structure of Cr is oriented in parallel to the surface of the substrate. When a Co alloy film is then formed by continuous operation of the film formation apparatus on the Cr film, that is, without interruption of the operation of the vacuum deposition or sputtering apparatus after completion of the formation of the Cr film, the bond length in the C axis of the hcp (hexagonal close packed) structure of the Co alloy film is substantially equal to the bond length in the (110) plane of the Cr film, so that the Co alloy film epitaxially grows in such a manner that the C axis may be in parallel with the surface of the substrate. Since the C axis of the hcp structure of this Co alloy film is an easy-to-magnetize axis, the Co alloy film constitutes an in-plane magnetizing film. The Cr film forming the base layer shows a relatively distinct structure of columnar grains and, therefore, the Co alloy film grown on the Cr film also has a granular structure in which grains are isolated from one another. As explained above, this two-layer film has a single-domain, granular structure having a crystalline magnetic anisotropy in the plane, with the result that a high coercive force is thus generated.
When there is no Cr film forming the base layer or when no epitaxial growth is possible on the Cr film due to contamination of the surface of the Cr film, the crystal grains in the Co alloy film are oriented vertically, resulting in a film known as a vertically magnetizing film.
As indicated in the foregoing, in a magnetic recording member of such an in-plane recording type, the Cr film forming the base layer serves to control the crystallization orientation and the granular shape formation of the Co alloy film, thus playing an extremely important role with respect to generation of the high coercive force.
Known Co alloy films such as the one described in the foregoing include those made of Co-Ni, Co-Ni-Cr, Co-Ni-Pt, Co-Cr, Co-Cr-Pt, Co-Ni-Zr, Co-Ni-W, Co-Cr-Ta, etc.